Photochromic glass nanoparticles and methods of preparation

Abstract

The present invention is directed to microemulsion techniques for rapidly preparing photochromic glass nanoparticles and to the photochromic glass nanoparticles so prepared. More particularly, the method of the invention comprises the combination of two microemulsions, one containing a water-soluble silver salt and a glass precursor and the other containing a halide salt and an initiator for glass formation, which process rapidly yields silver halide particles. This invention gives nanometer-sized silver halide particles embedded in glass, thus providing photochromic glass nanoparticles without further annealing, or at most mild annealing. These nanoparticles are valuable as added components to any macro-material that one might wish to have photochromic properties. The particles would impart photochromism while not affecting the physical properties of the material.

What is claimed is:  
     
       1. A method of preparing a photochromic glass nanoparticle, the method comprising: 
       obtaining a first precursor reverse microemulsion having micelles comprising a water-soluble silver salt and glass-forming components;  
       obtaining a second precursor reverse microemulsion having micelles comprising a halide salt and an initiator of glass formation;  
       a mixing the first and the second reverse microemulsions together such that the components of the micelles of the first precursor reverse microemulsion react with the components of the micelles of the second precursor reverse microemulsion;  
       to give a nanoparticle comprising one or more silver halide particles embedded in glass, the nanoparticle exhibiting a light-induced, reversible darkening. 
     
     
       2. A method according to  claim 1  wherein the soluble silver salt is silver nitrate and the halide salt is sodium chloride. 
     
     
       3. A method according to  claim 1  wherein the first precursor reverse microemulsion further comprises a water-soluble copper(I) salt. 
     
     
       4. A method according to  claim 1  which comprises the further step of adding a capping agent to the mixture of microemulsions after the nanoparticle has been formed. 
     
     
       5. A method according to  claim 4  which comprises the further step of adding a polymer or polymer precursor which reacts with the capping agent. 
     
     
       6. A method according to  claim 4  which comprises, following addition of the capping agent, the further steps of: 
       performing an aqueous extraction; and  
       collecting the nanoparticle from the aqueous phase.